This invention relates to an evacuation apparatus for a display device which is adapted to evacuate an envelope for the display device to a high vacuum, and more particularly to an evacuation apparatus which permits sealing and evacuation of the envelope of the display device to be consistently carried out.
Formation of a vacuum hermetic container for a display device such as a fluorescent display device or the like by sealing and evacuation is carried out by preliminarily calcining an envelope for the vacuum hermetic container, sealing the envelope in an inert gas atmosphere, evacuating the envelope through an evacuation section of the envelope to form a vacuum in the envelope and sealing the evacuation section, to thereby provide the vacuum hermetic container.
The above-described step of preliminarily calcining the envelope is executed at a calcination temperature of 200.degree. to 500.degree. C. to decompose an organic component of a sealing material. The sealing step is carried out at a calcination temperature of 300.degree. to 600.degree. C. to restrain generation of gas from a sealing material in an inert gas atmosphere, to thereby seal the envelope while pressedly holding the envelope by means of a clip or the like. Then, the envelope is evacuated to a high vacuum while being baked at a temperature which does not lead to re-melting of the sealing material, followed by sealing of the evacuation section.
The above-described steps may be carried out according to a chamber system wherein all the steps are in a single chamber or an in-line system wherein the steps are carried out in a plurality of rooms which are separated from each other through gate valves depending on an atmosphere and a temperature and through which the envelope is transferred by means of a carrier unit. Alternatively, a system may be employed which is adapted to carry out the sealing step and evacuation step in different units, respectively, wherein evacuation is carried out through the evacuation section and the remaining part of the envelope is exposed to an ambient atmosphere.
Conventionally, the evacuation section is constructed in two ways. In one of the ways, the evacuation section includes an exhaust pipe. In the other way, the evacuation section includes an evacuation hole comprising a through-hole formed via the envelope.
Now, the evacuation section of the latter type will be described hereinafter with reference to FIG. 5. An envelope 100 is formed by sealedly joining a front substrate 101 and a rear substrate 102 to each other through side substrates 103. An evacuation pipe 104 is arranged so as to communicate with an inner space of the envelope 100 and be led out of the the rear substrate 102. Evacuation of the envelope 100 is carried out through the evacuation pipe 104, which is then sealed by fusion.
The evacuation section of the former type is constructed in such a manner as shown in FIG. 6. An envelope 100 is formed by sealedly joining a front substrate 101 and a rear substrate 102 to each other through side substrates 103, like the envelope 100 shown in FIG. 5. Evacuation of the envelope 100 is carried out through an evacuation hole formed via the rear substrate 102 so as to communicate with an interior of the envelope 100 and then the evacuation hole 106 is sealedly covered with a lid 107 having an oxide solder 108 deposited thereon by fusing the solder.
Now, an in-line system for the sealing and evacuation which is disclosed in Japanese Patent Publication No. 39174/1992 by the assignee will be described with reference to FIG. 7.
First, a box-like casing formed by sealedly mounting side substrates on a front substrate is arranged on a rear substrate and is transferred to a preliminary calcination chamber 120 while pressedly holding the box-like envelope and rear substrate by means of a fixture such as a clip or the like for the purpose of forming an envelope. The preliminary calcination chamber 120 is provided therein with a heating unit, resulting in being kept at a temperature of 200.degree. to 300.degree. C. The calcination chamber 120 may have an ambient atmosphere introduced thereinto. Alternatively, it may have oxidizing gas introduced thereinto in order to carry out the preliminary calcination with increased efficiency. In the preliminary calcination chamber 120, an organic component contained in an oxide solder deposited on a sealing section of the envelope is fully subject to oxidation, resulting in being evaporated.
Upon completion of the preliminary calcination, a gate valve 121 is rendered open, so that a tray on which the envelope is put is guided to a gas substitution chamber 122 by a transfer unit. In the gas substitution chamber 122, gas therein is evacuated therefrom by means of a rotary pump 123 to cause gas in the envelope to be attendantly evacuated and then inert gas such as nitrogen gas, argon gas, carbon dioxide gas or the like is fed from an inert gas source 126 to the gas substitution chamber 122, to thereby cause the envelope to be charged with the inert gas.
Subsequently, the gate valve 124 is rendered open and the tray is transferred to the sealing furnace chamber 125. In the sealing furnace chamber 125, the envelope is heated to 300.degree. to 600.degree. C. in an inert gas atmosphere, so that the oxide solder deposited on the sealing section of the envelope is melted. The envelope is pressedly held by the fixture as described above, resulting in the front substrate and rear substrate being sealedly joined together. The sealing furnace chamber 125 is fed with inert gas from the inert gas source 126, to thereby prevent chemical change of cathodes and phosphors arranged in the envelope. Also, the feeding of the inert gas permits the whole envelope to be uniformly heated, to thereby substantially prevent generation of bubbles from the oxide solder.
The envelope thus sealed is then transferred to a slow cooling chamber 127 which is charged with the same inert gas as that of the sealing furnace chamber 125, in which the envelope is slowly cooled to a temperature of 200.degree. to 400.degree. C., so that the oxide solder is changed from a molten state to a solid state. The slowly cooled envelope is transferred to a roughing vacuum chamber 128 through gate valves 129 and 130 kept open by means of the transfer unit. The gate valve 129 is provided for heat sealing and the gate valve 130 is provided for vacuum formation. When the tray is transferred to the roughing vacuum chamber 128, a rotary pump 131 is operated to evacuate the chamber 128 to a low vacuum. When the chamber is thus evacuated to a predetermined vacuum, the gate valve 132 is rendered open, resulting in the tray being transferred to a main vacuum chamber 133. The main vacuum chamber 133 is kept evacuated to a high vacuum, so that even when a degree of vacuum due to opening of the gate valve 132 is reduced, operation of a diffusion pump 136 permits the main vacuum chamber 133 to be evacuated to a high vacuum in a short period of time. The main vacuum chamber 133 permits the envelope to be evacuated to a high vacuum. Then, a gate valve 135 is rendered open, so that the tray is transferred to a sealing chamber 134.
In the sealing chamber 134, the envelope is heated, so that gas is apt to be generated from the envelope. Concurrently, the diffusion pump 136 is kept actuated to evacuate the sealing chamber 134 to a high vacuum. Then, an evacuation pipe is sealed by fusion or an evacuation hole is sealed by melting an oxide solder deposited on a lid.
Thus, the envelope thus evacuated to a high vacuum is then transferred to a cooling chamber 138 through a gate valve 137 rendered open, followed by slow cooling in the cooling chamber 138. The envelope thus cooled is transferred to a takeoff chamber 140, in which it is further cooled and returned to an ambient pressure by leakage, followed by removal from the takeoff chamber 140.
The envelope removed from the takeoff chamber 140 is subject to gettering and aging, resulting in being completed.
Unfortunately, the in-line system described above requires evacuating a whole single room to a high vacuum, to thereby take a great deal of time for evacuation and a large-size installation for evacuation, resulting in deteriorating evacuation efficiency.
Also, evacuation of the whole single room to a high vacuum causes heat conduction in the atmosphere of the room to be deteriorated so as to render uniform heating for baking the envelope difficult, and thereby fail to fully carry out gas emission.
Further, the chamber system has problems as in the in-line system because it requires to evacuate the whole chamber in which evacuation and sealing are carried out to a high vacuum.